Exemplary embodiments of the present invention relate to a satellite-based SAR system and an emergency transmitter for such a SAR system.
A typical satellite-based system for supporting search and rescue services SAR (Search and Rescue) is the COSPAS/SARSAT system, which offers Doppler-based locating and also emergency radio. In the COSPAS/SARSAT system, emergency signals that are transmitted by emergency transmitters on the international emergency frequencies 121.5 MHz, 243 MHz, and 406 MHz are relayed via special transponders on board satellites to ground stations LUT (Local User Terminal), and the received emergency signals and the data contained therein are transferred to a control center MCC (Mission Control Center), which determines rescue measures that are then executed by a rescue coordination center (RCC). LEO (Low Earth Orbit) satellites and GEO (Geostationary Earth Orbit) satellites are used as carriers for the transponders. In order to be able to ensure an even better reception of emergency calls it is also planned to include satellites of the future European satellite navigation system Galileo in the COSPAS/SARSAT system.
In its newest version, an emergency transmitter also transfers position data, determined through NAVSTAR-GPS, of a transmitter in an emergency situation, for example of an aircraft, ship or a person, to the ground station LUT of the COSPAS/SARSAT system. In this manner, localization of the transmitter in distress can be improved with respect to the locating carried out based on conventional Doppler locating. However, this requires that the emergency transmitter still functions after triggering an emergency call and that a connection to the satellite of the COSPAS/SARSAT system can be established, which, for example, is in most cases not possible after crashes of small aircrafts because very often, these aircrafts lie in such a problematic terrain that the satellites can no longer be contacted.
This shortcoming is partially overcome by the so-called SPOT (Satellite Personal Tracker) messenger recently launched by the Canadian enterprise SPOT Inc. In a special operating mode, an activated SPOT messenger transmits its position data, determined by means of NAVSTAR-GPS, approximately every 10 minutes to a database application that makes this position accessible for authorized users through a web interface. However, the period of approximately 10 minutes between the transfers of the position of the SPOT satellite messenger and the low reliability of the individual transfers can result in the actual time intervals between the positions known in the database application becoming very long, and therefore also the search area in an emergency case becomes very large. Up to now, a search is triggered when the user pushes the emergency button on the SPOT emergency unit or, if the aircraft is overdue, an authorized user of the database application transmits the latest position stored in the database application to the search and rescue service. In many cases, the emergency transmitter becomes inoperable during the crash so that this second way would be frequently needed. However, this can only take place if an authorized person considers the aircraft as being overdue, which is often the case only several hours after the accident.
Exemplary embodiments of the present invention provide improved satellite-based SAR services that provide a smaller search area in an emergency.
In accordance with the present invention an emergency transmitter reports its position to a satellite at a specified time calculated depending on the orbit and the position of the satellite and the emergency transmitter's own position, and if no position reports from an emergency transmitter are received within a specified time after receipt of the last position report, the SAR system initiates a rescue action if the emergency transmitter is not logged out of the system. In this manner the search area in an emergency case can be limited to a relatively small area while alerting still works when the emergency transmitter has been destroyed, so that safety can be significantly improved with the SAR system according to the invention.
According to one embodiment, the invention relates to a satellite-based SAR system having a space segment with a plurality of satellites and a ground segment with one or a plurality of ground stations, wherein
a satellite receives a position report from an emergency transmitter in its service area and forwards it to a ground station, and stores in each case the last reported position and time of the emergency transmitter until the satellite can forward the position to a ground station,
the ground station stores the emergency transmitter's position, received with the last position report, in a management system for emergency transmitters,
the emergency transmitter sends position reports to satellites such that the reception of position reports at the satellite are coordinated in such a manner that at any time only position reports are received that differ with regard to their signal parameters such that simultaneous reception is possible, and
a rescue operation is initiated for the emergency transmitter if no deactivation message has been received from the emergency transmitter and no position report is received from the emergency transmitter within a specified period.
Furthermore, a data message with the expected time at which the next position report from the emergency transmitter is to be received at a satellite can be transmitted to the emergency transmitter, and/or a data message with at least one parameter for an algorithm, according to which the individual emergency transmitters can calculate the planned reception times of their messages at the satellite and the signal parameters used for this purpose, can be transmitted simultaneously to a multiplicity of emergency transmitters in the service area, and
the emergency transmitter can determine the position of the satellite based on the information contained in the received data message and, with the position of the satellite and its own position, can calculate when the next position report is to be sent to the satellite such that the position report is received by the satellite at the expected time.
After receiving the position report from the emergency transmitter, the data message can be transmitted by the satellite or also via a different medium. The emergency transmitter can determine the orbit of a satellite based on Doppler measurements of signals of the satellite and use the orbit for determining the position of the satellite. Alternatively, it is also possible to transmit the orbit together with the data message to the emergency transmitter so that the emergency transmitter itself does not have to determine the orbit.
For the purpose of deactivation, the emergency transmitter can send a deactivation message to the space segment, and after receiving the deactivation message, the logout of the emergency transmitter from the management system can be initiated, and after logging out, a logout message can be transmitted via the space segment to the emergency transmitter which deactivates upon receiving this message.
Furthermore, a data message may contain a specified coding with which the next position report from the emergency transmitter is to be received, wherein the specified coding comprises in particular a specified frequency, a specified modulation and/or a specified message content.
The expected time contained in a data message can be determined such that at the expected time, the satellite sending the data message is still within the reception range of the emergency transmitter.
The time difference between time of sending a data message and the expected time contained in the data message can be at most approximately 5 minutes, in particular less than 5 minutes.
Initiating a rescue operation for an emergency transmitter can comprise transmitting a rescue message from the management system to a rescue coordination center in the vicinity of the emergency transmitter's last position stored in the management system.
In another embodiment, the invention relates to an emergency transmitter for a satellite-based SAR system according to the invention and as described above, comprising
a transceiver for sending and receiving messages to and from, respectively, satellites of the space segment of the SAR system,
a position determining unit for determining the actual position of the emergency transmitter, and
a control unit for generating and sending position reports via the transceiver, and receiving and processing data messages at and from, respectively, satellites of the space segment of the SAR system.
The position determining unit can comprise a receiver for navigation signals of a satellite navigation system and a processor for calculating the actual position from the received navigation signals.
The control unit can be configured such that it determines, based on the information contained in a received data message, the position of a satellite that sent the data message, and calculates, using the position of the satellite and the actual position of the emergency transmitter, when the next position report is to be sent to the satellite, and sends at the calculated time the next position report with the now actual position of the emergency transmitter via the transceiver to the satellite.
Furthermore, the control unit can be configured such that based on the specified coding, which is contained in the received data and with which the next position report from the emergency transmitter is to be received, the control unit controls how the next position report is sent to a satellite, wherein the specified coding comprises a specified frequency, a specified modulation and/or a specified message content, and the control unit controls, according to the specification, the frequency, the modulation or the message content of the next position report to be sent.
Further advantages and possibilities of use of the present invention arise from the following description in connection with the exemplary embodiments illustrated in the drawings.
In the description, the claims, the abstract, and the drawings, the terms and associated reference numbers used in the reference list set out at the end are used.